In general, it can be stated that, in the case of bearing trees, the longer the shoot growth and the greater its diameter in proportion to length, the greater is the number of pistillate flowers that may be formed at its terminal. Furthermore, the set of nuts and the size that they attain are in proportion to the length and diameter of the shoots bearing them. In other words, the number of flowers formed, the nuts set, and the size that they attain are directly correlated with the vigor and growth of the trees. As trees attain age, fewer long, strong shoots and more short, weak shoots are formed. Hence the average size of the nuts produced decreases because of the reduction in average shoot growth. Furthermore, under normal conditions, the degree to which the nuts are filled is related to the vigor as it is measured by the length and diameter of the shoots bearing them. Strong, vigorous shoots usually produce the best filled and earliest maturing nuts.
+What Is a Nut and of What Does It Consist?+
Webster gives a general definition of a nut as "a fruit consisting of a kernel or seed enclosed in a hard woody or leathery shell that does not open when ripe, as in the hazel, beech, oak, chestnut." Technically speaking, it is a hard, indehiscent, one-seeded dry fruit resulting from a compound ovary. In horticultural language the fruit consists of the hard or leathery nut containing a kernel, together with the husk, hull, or bur that surrounds the nut shell. This kernel consists of the embryo plus the endosperm or its remains. In all of our important nuts, such as walnuts, pecans, hickory nuts, almonds, and filberts, the kernel is essentially the embryo with its thickened cotyledons or seed leaves, as the endosperm has been absorbed except for a thin membrane.
At the beginning of its development, growth of the embryo is slow, and in very early stages it is merely a rounded mass of cells. Later, the meristems of the epicotyl (stem or top) and root axis develop, but the whole embryo is still microscopic in size. Still later the cotyledons (seed leaves) start development from the apical meristem and their growth in length is rapid, but they are very thin and follow the contours of the seed coat. Growth in length of the cotyledons may be arrested by unfavorable nutritional conditions during the time of elongation. In such case, the lobes of the cotyledons may not attain the full length of the seed coat, or pellicle, which surrounds them. After the cotyledons have attained full length, growth in thickness begins in the area nearest the epicotyl and proceeds toward the margins. This growth in thickness results from cambium-like meristem with the formation of new cells. The formation of well developed or solid kernels that completely fill the cavity within the shell is dependent upon meristematic activity continuing almost to maturity. The weather conditions, the nutrition of the tree, or other factors that affect the synthesis and translocation of elaborated food materials from the leaves and shoots to the kernels at this time determine the degree to which the cotyledons are thickened, or in other words how well the nuts are filled.